Adium

Adium is a free and open source instant messaging application for OS X, written using OS X's Cocoa API, released under the GNU GPL and developed by the Adium team. Based on the libpurple protocol library, Adium can connect you to any number of messaging accounts on any combination of supported messaging services and then chat with other people using those services.

Features

• Open Source, so everyone can see how Adium works and help improve it.
• Support for a wide range of different Instant Messaging services (see the full list)
• A delightful UI
• Tabbed chat windows
• macOS system integration
• Address Book integration
• WebKit Message View: Theme your chat windows
• Combined Contacts: Merge your contacts so that each one represents a person, not an account
• A sophisticated events system (including Growl notifications)
• OTR Encryption
• File Transfer
• Xtras and many, many other customization options
• A beautiful icon, the "Adiumy" duck
• Translations: Adium speaks 27 different languages

System requirements

• Adium 1.5 or later: Mac OS X 10.6.8 or newer, an Apple-branded Macintosh computer
• Adium 1.4.5: Mac OS X 10.5.8
• Adium 1.3.10: Mac OS X 10.4
• Adium 1.0.6: Mac OS X 10.3.9
• Adium X 0.89.1: Mac OS X 10.2.x and older
• Adium X 0.88 up to Adium 1.4.5 are Universal applications which run natively on both PowerPC- and Intel-based Macintosh computers. Adium 1.5 and up require an Intel based computer.